1. Field of the Invention
The present invention relates to a nitride semiconductor light-emitting device.
2. Description of the Background Art
Nitride semiconductors are very useful as a light-emitting device such as a light-emitting diode (LED) or a laser diode (LD) owing to their property of emitting light over a wide range that covers the entire region of visible light as well as the ultraviolet region. A nitride semiconductor light-emitting device mainly includes an n side electrode, an n type nitride semiconductor layer, a light-emitting layer, a p type nitride semiconductor layer, and a p side electrode.
One problem with a nitride semiconductor light-emitting device is that it is difficult to obtain a p type nitride semiconductor layer of high carrier concentration because activation energy of a p type dopant is high. Contact resistance between the p type nitride semiconductor layer and the p side electrode formed of metal, a translucent conductive layer or the like thus increases, resulting in a higher operating voltage of the nitride semiconductor light-emitting device.
Methods for solving this problem have conventionally been proposed. For the p type nitride semiconductor layer, it has been proposed to use p type InGaN that can be formed to have high carrier concentration as a layer in contact with the p side electrode, or to increase Mg concentration. For the p side electrode, it has been proposed to select a metal of high work function such as Pd or Ni when metal is used, or to devise annealing conditions after forming a translucent conductive layer when a translucent conductive layer is used.
Another problem with a nitride semiconductor light-emitting device is that in a light-emitting diode including a p type nitride semiconductor layer and a translucent conductive layer in contact with each other, total reflection may occur at a contact interface between them because a nitride semiconductor layer has a high refractive index of about 2.5, for example. This results in lower luminous efficiency.
In order to solve this problem, Japanese Patent Laying-Open No. 2005-277374 proposes a method of forming a concave-convex surface of a p type nitride semiconductor layer, which causes scattering and diffraction to reduce the amount of total reflection, thereby improving light extraction efficiency.